Background: The DSM-IV age at onset criterion for attention-deficit/hyperactivity disorder (ADHD) has been a subject of debate. In DSM-5, the required age at onset (ie, the age by which impairing symptoms must have been present) has increased from 7 years to 12 years. The present study examined measurement properties of ADHD symptoms according to age at onset.

Method: Data were derived from the 2004–2005 National Epidemiologic Survey on Alcohol and Related Conditions, which included 34,653 US participants. Among participants with a lifetime DSM-IV diagnosis of ADHD (assessed using the Alcohol Use Disorder and Associated Disabilities Interview Schedule-IV), we compared the psychometric properties of the 18 ADHD symptoms according to 3 categories of age at onset (≤7 years, >7 and ≤12 years, and >12 and ≤18 years). A 2-parameter item response model was used to estimate differential item functioning (DIF) between these groups.

Results: 364 participants with a lifetime DSM-IV diagnosis of ADHD had an age at onset ≤7 years, 252 had an age at onset >7 and ≤12 years, and 148 had an age at onset >12 and ≤18 years. In both dimensions of ADHD (ie, inattention and hyperactivity-impulsivity), there was no significant DIF between age at onset groups.

Conclusions: Expression of DSM-IV ADHD symptoms was not affected by age at onset in the 3 groups considered. This study provides psychometric support to the change in the age criterion introduced by DSM-5 and further suggests that the age at onset criterion could be extended to 18 years without changing the psychometric properties of the ADHD symptoms.